Previously, cholesta-1,5,7-trien-3-ol has been prepared by the base-catalyzed rearrangement of cholesta1,4,6-trien-3-one to isomerize the 4,6-diene to the 5,7-diene, followed by the reduction of the formed cholesta-1,5,7-trien-3-one (C. Kaneko et al., Tetrahedron, 30, 2701, 1974 and D. W. Guest et al., J Chem. Soc., Perkin I, 1979, 1695). In that case, however, the yield of cholesta-1,5,7-trien-3-ol is about 25 to about 40%. Thus, there was such a drawback that so far as the final product, 1.alpha.-hydroxyvitamin D.sub.3 is synthesized via the steps of the prior arts as referred to above, the yield of the final product will considerably be low and moreover, much time and labor are required for the purification and isolation of the desired product.
Under such circumstances, it has been ardently desired to prepare cholesta-1,5,7-trien-3-ol, the intermediate for the synthesis of 1.alpha.-hydroxyvitamin D.sub.3, in more favorable yields by an economical and efficient way.